[boathead]

I am trying to set up a conjugate heat transfer model (in the case of the attached image, just a simplified version of the main model). The model has 4 separate regions; the solid plate in the middle, the top box, the bottom box and the tube in the middle. Fluid is supposed to flow through up through the bottom box, through the tube and into the top box where there is a crossflow (left to right).

I am trying to incorporate two separate physics continua, one for the top box and one for the bottom box because I need to specifiy different pressure and viscosity boundary conditions at A and B respectively. At both A and B I am using a velocity inlet as my boundary condition which is why I cannot use one physics continuum.

The problem I am having is that, having created all the necessary interfaces between the fluid and solid regions and the fluid to fluid regions (i.e the top and bottom of the tube with the wall of the top and bottom boxes), when I apply physics continuum 1 to the top box and physics continuum 2 to the bottom box and leave the tube without (or with physics 1 or 2) no physics continuum, (depending on which physics continuum is applied to which region) it will change either the interface at the top (highlighted by the red circle) or bottom of the tube from an internal interface to a baffle which means the fluid will not go through it. I cannot even change it from a baffle back to an internal interface which is frustrating!

Is it possible to have two physics continua in such a case and if so what is the best way to get around the baffle issue.

Cheers